Process of malleableizing iron



Mach :5, 1924.

T. CHANDLER PROCESS OF MALLEABLEIZING IRON 'i'iled Nov. 14, 1921Patented Mar. 25, 1924.

HENRY T. CHANDLER, 0F MARYSVILLE, MICHIGAN.

PROCESS OF MALLEAIBLEIZING IRON.

Application filed November 14, 1921.

To all whom it may concern.

Be it known that I, HENRY THOMAS CHANDLER, a citizen of the UnitedStates of America, residing at Marysville, in the county of St. Clairand State of Michigan, have invented certain new and useful Improvementsin Processes of 'Malleableizing Iron, of which the following is aspecifica-.

tion, reference being had therein to the accompanying drawings.

Commercially, the manufacture of malleable iron is conducted in twosteps. The first of vthese includes melting, molding, casting and otherfoundry operations incident to the production of suitable white ironcastings. The second step consists in the conversion of these hard,brittle, unmachineable castings, by a suitable thermal treatment, intosoft, malleable'and commercially useful products.

This invention relates particularly to this commercial method ofannealing.

Metallurgically, white iron, suitable for malleableizing, consists of amixture of iron carbide, known as cementite, and an alloy of. ironcarbide and iron. The properties of these constituents and theirdistribution within the casting account for the brittleness and otherphysical characteristics of the metal. This system, in which the carbonall exists in chemical combination, is me tastable; in other words, itis permanent not because actual chemical equilibrium exists, but becausefurther molecular re-arrangement is impossible under the temperatureconditions obtaining. It is the purpose of annealing to convert, by theeffect of time and temperature, this metastable system of iron carbideand iron into the stable system consisting of iron and free carbon(graphite), accomplishing thereby a change in the nature andre-arrangement of the constitu- Serial No. 514,844.

cuts of the casting resulting in a commercially useful product.

Annealing practice, as usually carried out, consists first in packingthe castings together with either an inert or chemically activematerial, such as mill scale, slag, iron ore and the like, in cast ironor other pots. Various sizes and forms of containers and kinds ofpacking materials are used, depending largely upon the work to betreated and to some extent upon the nature of the equipment availableand personal opinion of the annealer. The purpose of packing isprimarily to support the castings while hot and thus prevent sagging ordistortion under their own weight or the weight of the cast ings abovethem. It also serves as a protection for the castings from scaling orother effects of the combustion gases and further, due to mass, has astabilizing effect upon temperature, preventing rapid changes harmful tothis process. Packing has no significant effect upon the graphitizingreactions proper.

The pots containing the castings are then stacked and charged into theannealing ovens. These ovens are usually very simply constructed andhand fired with coal. They .may hold from twenty-five to one hundredstacks of pots; neither extreme, however, is common practice. The doorsare sealed and the oven and its contents are brought to a maximumtemperature of from about 1500 to 1850 degrees Fahrenheit. heat-ing ischemically unimportant and is limited by the .nature of the oven and thedisposition of the charge within.

Temperature is maintained for a period of from a few hours to severaldays, to effect thorough heating'of the charge and permit the initialreactions within the castings to attain equilibrium. When this isaccomplished, firing is stopped and the oven and contents allowed tocool. The cooling rate is important and the ovens are so built that thisdoes not exceed 10 to 15 degrees per hour throughout the critical range.After cooling to from 1000 degrees Fahrenheit to around 200 degreesFahrenheit, depending largely upon the means available for removing thework, the pots are removed and the The rate of castings cleaned. afterwhich they are ready I i the A,

its large size,- second,

cases, over two weeks. Widevariationsin denecessary to avoid scaling;and third, to the tail are practiced in different foundries, due,mechanical equipment necessary to effect the no doubt, to the fact thatthe art of producmovement of the charge through the furing malleableiron preceded by over a hunnace. Furnaces of this type can only be dredyears an understanding of thechemistry eliicient when constantlyoperating at full of graphitization. 1 or nearly full capacity, andtherefore lack In all instances, however, the complete the flexibilitydemanded in the usual jobprocess may be divided into the following bingfoundry. I fourintervals, the first two of which being In the stationarytype of mufile furnace, heating and the last two cooling operations:packing is also either totally or partially 1st, Heating to sometemperature above eliminated, and the cooling cycle becomes point. i aquestion cf furnace control. 2nd. Holding at this temperature for alVith my improved process, instead of carperiod of time. rylng out thecomplete operation'in one ag- 3rd. Cooling to below the A point at aparatus, the heating and cooling steps oft 0 slow rate. V 7 treatmentare separated and accomplished 4th. Further cooling to permit handling.in different enclosures, the heating being These four parts of theannealing cycle carried on in a furnace which is adapted for arecompleted in a single furnace or anneal efiiclently carrying "out thisoperation and ing chamber, substantially as outlined abovei he Workbeing then transferred to an an- The process, thus conducted, whencomparatus constructed to etficiently effect t e pared with analogousmetallurgicalo eranecessary cooling cycle. The process is tions, is v ryineffi i nt This is du fir t. based z first, on the discovery thatchemically to the fact that an oven which will have the the rate ofheating is immaterial; secon l li h t i ti cessary for the that thehigher the initial temperature is successful completion of the process,is not ralsed above the critical point, the more a construction suitablefor the eflicient heat rapidly is chemical equilibrium established; ingof the work either as regards time or third, that the rate of coolingisimmaterial, fuel economy; second, the oven operates as excepting througha narrow temperature a heating unit during but a small part of therange, and; fourth, that the initial temperatime necessary for thecomplete cycle; third, ture may be considerably higher than this theextreme range of temperature to which range. 7 the oven is subjectedresults in rapid de- The conditions being such, the transfer ofterioration and heavy upkeep expenses." work to the cooling chamber maybe accom- Initial installation, upkeep and overhead plished withoutdetriment to the reactions costs must, therefore, be met on an apparaofgraphitization, it being only necessary tus svhich is idle a greaterpart of the time that the initial temperature should be sufliinperforming one of its major functions, ciently high to avoid droppingbelow this which is subjected to temperature extremes, critical rangeduring transfer. causing rapid deterioration due to expan- The specificform of apparatus required sion and contraction of the brick work, and,forthe carrying out of my improved rocess due to the great length oftime necessary to may be varied, but as diagrammatical y repcomplete'theprocess, is limited in its outresented in the drawings,

ut. The direct result of these conditions is that'only the most simpleand cheap conheating furnace; and structions are economically practical,and Figure 2 is a similar view through the more eliicient furnaces andmethods of fuel cooling chamber. utilization, through almost universallyused As shown, A is a furnace suitably conin allied practice, are hereruled out on the: structed for the eflicient heating of the work basisof cost. r placed 'in thechamber. The furnace may be a More recentdevelopment has contemplatof the car type in which the work is placed edthe use of electricity as a source of heat *upon trucks B which aremeva-ble into and or the use of mufiie furnaces of either the out fromthe furnace, or any other cou= stationary or tunnel type, in order toavoid venient means'of transporation may be propacking and thus speed upthe process to avided. C is the cooling chamber which dif- Figure lis across section through the point where the use of such equipment befersradically in its construction from A so 7 comes of economic value; as tobe efficient in the control of the coolin the tunnel furnaces the workis grading of the work. If the work is placed on ually advanced, firstpassing through a zone trucks, these may be transferred from the inwhich the proper temperature is reached heating furnace *A to thecooling chamber C and maintained and then through portions and these twoparts of the apparatus may at progressively lower temperatures to combelocated in any convenient relation to each pletion. Such a type ofapparatus is necesother. Cooling may be controlled by the v sariiyinitially very expensive, due; first, to use of suitable dampers for theadmission of t e mufile construction hot waste gases from the meltingfurnaces or heating oven, or the use of an individual heating equipment,or combinations of these. In place of cooling of the product of theheating chamber in a single cooling chamber, two or more of these may beused, if desired.

The essential feature of the apparatus is that the cooling chamber shallnot interfere with the efiicient functioning of the heating furnace andthat the heating furnace shall not interfere with efficient functioningof the cooling chamber.

In operation, the higher the temperature in the heating furnace withoutdetriment to the work, the more rapidly is equilibrium established inthe initial reaction, and the shorter the time interval required forthis step of the treatment. The work is there fore placed in the heatingfurnace and permitted to remain for an interval varying with thetemperature and with other conditions, such as the analysis of the iron,the manner of packing, etc. The work is then transferred to theannealing furnace and the rate of cooling controlled until the low pointof the critical range is reached, after which it maybe removed.

The time required for the complete process as thus carried out is verymuch less than with the usual practice, as not only is heating effectedmore rapidly than in usual practice, but also the very slow coolingnecessary to the reaction is carried out only within the range in whichit is effective.

The economies of the process are many, among which may be cited thefollowing:

First, the heating furnace is operated continuously as a heating unitwithin a comparatively narrow temperature range, thus varying fuelconsumption; I

Second, he cooling chambers are of very simple and cheap constructionand are capable of long service, as they are not subjected to eitherexcessive temperature or change of temperature;

Third, due to the resulting shorter time cycle, the output of theannealing equipment is increased and the overhead burden borne by thecharge is reduced;

Fourth, installation costs are low when compared either with the usualpractice or the use of tunnel and muflle furnaces.

W'hat I claim as my invention is:

1. The method of malleableizing iron which consists in. heating the workin one enclosure and in cooling the work in a separate enclosure.

2. The method of malleableizing iron which consists in heating'the workin a fur nace adapted for the efiicient accomplishment of suchoperation, in cooling the work .in a separate chamber and intransferring the work from theone to the other while at a temperatureabove the critical point.

3. The method of malleableizing iron which consists in heating the workin a furnace adapted for eflicient and rapid elevation of temperature toabove the critical point for the primary reaction, in maintaining thetemperature above such point until the equilibrium of the primaryreaction is established, in transferring the work while at a temperaturestill above said critical range to a separate cooling chamber and incontrolling the rate of cooling through the low point of the criticalrange.

4. The method of malleableizing iron which consists in elevating thetemperature of the work rapidly to above the critical point (A,) forinitiating the primary reaction, in a furnace adapted for eflicientlyaccomplishing such treatment, in transferring the work while still abovethe critical temperature to a cooling chamber and in controlling thecooling process at the required rate through thecritical range. v

5. The method of malleableizing iron which consists in heating the workwhile stationary in one enclosure, in transferring the work to aseparate enclosure, and cooling the work while stationary in the latterenclosure.

6. The method of malleableizing iron which consists in heating the workwhile stationary in a furnace adapted for the eflicientaccomplishment ofsuch operation, in transferring the work while at a temperature abovethe critical point to a separate chamber adapted for controlling therate of cooling and cooling the working in said chamber at-apredetermined rate through the low point of the critical range whilesaid work is stationary therein.

7 The method of malleableizing iron which consists in placing the workin a furnace adapted for efiicient and rapid elevation of temperature toabove the critical point for the primary reaction, in maintaining thework stationary in said furnace at a temperature above such point untilequilibrium of the primary reactionis 'es tablished, in transferring thework while at a temperature still above said critical range to aseparate cooling chamber, and in controlling the rate of cooling throughthe low point'of the critical range while maintaining the workstationary in said chamber.

In testimony whereof I afiix my signaturea HENRY T. CHANDLER.

